Rectangular block transform scaling

ABSTRACT

A device for decoding video data determines a quantization parameter (QP) for a block of transform coefficients, wherein the block of transform coefficients is a non-square, rectangular block; determines a value for (log 2  (width)+log 2  (height), wherein width represents a width of the block of transform coefficients and height represents a height of the block of transform coefficients; in response to the value not being divisible by 2, determines a modified QP for the block of transform coefficients based on the QP; inverse transforms the transform coefficients to determine a block of quantized residual samples; and dequantizes the quantized residual samples based on the modified QP to determine a block of residual samples.

This application claims the benefit of U.S. Provisional PatentApplication 62/738,947, filed 28 Sep. 2018, the entire content of whichis hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard, ITU-TH.265/High Efficiency Video Coding (HEVC), and extensions of suchstandards. The video devices may transmit, receive, encode, decode,and/or store digital video information more efficiently by implementingsuch video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

This disclosure describes an alternative scaling scheme usingquantization parameter (QP) offsets for certain aspect ratio rectangulartransforms.

In one example, a method for decoding video data includes determining aquantization parameter (QP) for a block of transform coefficients,wherein the block of transform coefficients is a non-square, rectangularblock; determining that a value for (log₂ (width)+log₂ (height) is notdivisible by 2, wherein width represents a width of the block oftransform coefficients and height represents a height of the block oftransform coefficients; in response to the value not being divisible by2, determining a modified QP for the block of transform coefficientsbased on the QP; inverse transforming the transform coefficients todetermine a block of quantized residual samples; and dequantizing thequantized residual samples based on the modified QP to determine a blockof residual samples.

According to another example, a device for decoding includes a memoryconfigured to store video data and one or more processors implemented incircuitry and configured to determine a quantization parameter (QP) fora block of transform coefficients, wherein the block of transformcoefficients is a non-square, rectangular block; determine that a valuefor (log₂ (width)+log₂ (height) is not divisible by 2, wherein widthrepresents a width of the block of transform coefficients and heightrepresents a height of the block of transform coefficients; in responseto the value not being divisible by 2, determine a modified QP for theblock of transform coefficients based on the QP; inverse transform thetransform coefficients to determine a block of quantized residualsamples; and dequantize the quantized residual samples based on themodified QP to determine a block of residual samples.

According to another example, a computer-readable storage medium storesinstructions that when executed by one or more processors cause the oneor more processors to determine a quantization parameter (QP) for ablock of transform coefficients, wherein the block of transformcoefficients is a non-square, rectangular block; determine that a valuefor (log₂ (width)+log₂ (height) is not divisible by 2, wherein widthrepresents a width of the block of transform coefficients and heightrepresents a height of the block of transform coefficients; in responseto the value not being divisible by 2, determine a modified QP for theblock of transform coefficients based on the QP; inverse transform thetransform coefficients to determine a block of quantized residualsamples; and dequantize the quantized residual samples based on themodified QP to determine a block of residual samples.

According to another example, an apparatus for decoding video dataincludes means for determining a quantization parameter (QP) for a blockof transform coefficients, wherein the block of transform coefficientsis a non-square, rectangular block; means for determining that a valuefor (log₂ (width)+log₂ (height) is not divisible by 2, wherein widthrepresents a width of the block of transform coefficients and heightrepresents a height of the block of transform coefficients; means fordetermining a modified QP for the block of transform coefficients basedon the QP in response to the value not being divisible by 2; means forinverse transforming the transform coefficients to determine a block ofquantized residual samples; and means for dequantizing the quantizedresidual samples based on the modified QP to determine a block ofresidual samples.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example process for encoding acurrent block.

FIG. 6 is a flowchart illustrating an example process for decoding acurrent block.

FIG. 7 is a flowchart illustrating an example process for decoding videodata.

DETAILED DESCRIPTION

Video coding (e.g., video encoding and/or video decoding) typicallyinvolves predicting a block of video data from either an already codedblock of video data in the same picture (e.g., intra prediction or intrablock copy) or an already coded block of video data in a differentpicture (e.g., inter prediction). In some instances, the video encoderalso calculates residual data by comparing the predictive block to theoriginal block. Thus, the residual data represents a difference betweenthe predictive block and the original block of video data. To reduce thenumber of bits needed to signal the residual data, the video encodertransforms and quantizes the residual data and signals the transformedand quantized residual data in the encoded bitstream. The compressionachieved by the transform and quantization processes may be lossy,meaning that transform and quantization processes may introducedistortion when the encoded video data is decoded.

A video decoder decodes and adds the residual data to the predictiveblock to produce a reconstructed video block that matches the originalvideo block more closely than the predictive block alone. Due to theloss introduced by the transforming and quantizing of the residual data,the reconstructed block may have distortion or artifacts. One commontype of artifact or distortion is referred to as blockiness, where theboundaries of the blocks used to code the video data are visible.

To further improve the quality of decoded video, a video decoder canperform one or more filtering operations on the reconstructed videoblocks. Examples of these filtering operations include deblockingfiltering, sample adaptive offset (SAO) filtering, and adaptive loopfiltering (ALF). Parameters for these filtering operations may either bedetermined by a video encoder and explicitly signaled in the encodedvideo bitstream or may be implicitly determined by a video decoderwithout needing the parameters to be explicitly signaled in the encodedvideo bitstream.

As introduced above, a video encoder transforms residual data to producetransform coefficients. Those transform coefficients may additionally bequantized. In this disclosure, the term transform coefficient, orcoefficient, may refer to either a quantized transform coefficient or anunquantized transform coefficient. This disclosure describes techniquesfor determining a modified quantization parameter (QP) for rectangularblocks with certain aspect ratios. As described in more detail below,the techniques of this disclosure may reduce the bit depth ofintermediate values determined during the quantization anddequantization processes, which may reduce memory bandwidth and overallcomputational complexity. Reducing memory bandwidth and overallcomputational complexity may improve overall device performance.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,uncoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may be any of a widerange of devices, including desktop computers, notebook (i.e., laptop)computers, tablet computers, set-top boxes, telephone handsets such assmartphones, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, source device 102 and destination device 116 may be equippedfor wireless communication, and thus may be referred to as wirelesscommunication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for rectangularblock transform scaling described in this disclosure. Thus, sourcedevice 102 represents an example of a video encoding device, whiledestination device 116 represents an example of a video decoding device.In other examples, a source device and a destination device may includeother components or arrangements. For example, source device 102 mayreceive video data from an external video source, such as an externalcamera. Likewise, destination device 116 may interface with an externaldisplay device, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forrectangular block transform scaling. Source device 102 and destinationdevice 116 are merely examples of such coding devices in which sourcedevice 102 generates coded video data for transmission to destinationdevice 116. This disclosure refers to a “coding” device as a device thatperforms coding (encoding and/or decoding) of data. Thus, video encoder200 and video decoder 300 represent examples of coding devices, inparticular, a video encoder and a video decoder, respectively. In someexamples, source devices 102 and destination device 116 may operate in asubstantially symmetrical manner such that each of source devices 102and destination device 116 include video encoding and decodingcomponents. Hence, system 100 may support one-way or two-way videotransmission between source devices 102 and destination device 116,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

In general, video source 104 represents a source of video data (i.e.,raw, uncoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some example, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memories 106 and 120 are shown separately fromvideo encoder 200 and video decoder 300 in this example, it should beunderstood that video encoder 200 and video decoder 300 may also includeinternal memories for functionally similar or equivalent purposes.Furthermore, memories 106 and 120 may store encoded video data, e.g.,output from video encoder 200 and input to video decoder 300. In someexamples, portions of memories 106, 120 may be allocated as one or morevideo buffers, e.g., to store raw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium mayinclude one or both of a wireless or wired communication medium, such asa radio frequency (RF) spectrum or one or more physical transmissionlines. The communication medium may form part of a packet-based network,such as a local area network, a wide-area network, or a global networksuch as the Internet. The communication medium may include routers,switches, base stations, or any other equipment that may be useful tofacilitate communication from source device 102 to destination device116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 include wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 includes a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream from computer-readable medium 110 may include signalinginformation defined by video encoder 200, which is also used by videodecoder 300, such as syntax elements having values that describecharacteristics and/or processing of video blocks or other coded units(e.g., slices, pictures, groups of pictures, sequences, or the like).Display device 118 displays decoded pictures of the decoded video datato a user. Display device 118 may represent any of a variety of displaydevices such as a cathode ray tube (CRT), a liquid crystal display(LCD), a plasma display, an organic light emitting diode (OLED) display,or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may include an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM). It is contemplated that video encoder 200 and video decoder300 may also be configured to operate according to the Versatile VideoCoding (VVC) standard presently under development. A recent draft of VVCis available fromhttp://phenix.it-sudparis.eu/jvet/doc_end_user/documents/11_Ljubljana/wg11/JVET-K1001-v5.zip.The techniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM. According to JEM, a video coder(such as video encoder 200) partitions a picture into a plurality ofCTUs. Video encoder 200 may partition a CTU according to a treestructure, such as a quadtree-binary tree (QTBT) structure. The QTBTstructure of JEM removes the concepts of multiple partition types, suchas the separation between CUs, PUs, and TUs of HEVC. A QTBT structure ofJEM includes two levels: a first level partitioned according to quadtreepartitioning, and a second level partitioned according to binary treepartitioning. A root node of the QTBT structure corresponds to a CTU.Leaf nodes of the binary trees correspond to coding units (CUs).

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT structure to represent each of the luminance and chrominancecomponents, while in other examples, video encoder 200 and video decoder300 may use two or more QTBT structures, such as one QTBT structure forthe luminance component and another QTBT structure for both chrominancecomponents (or two QTBT structures for respective chrominancecomponents).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning according to JEM, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay include N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

JEM also provides an affine motion compensation mode, which may beconsidered an inter-prediction mode. In affine motion compensation mode,video encoder 200 may determine two or more motion vectors thatrepresent non-translational motion, such as zoom in or out, rotation,perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. JEM providessixty-seven intra-prediction modes, including various directional modes,as well as planar mode and DC mode. In general, video encoder 200selects an intra-prediction mode that describes neighboring samples to acurrent block (e.g., a block of a CU) from which to predict samples ofthe current block. Such samples may generally be above, above and to theleft, or to the left of the current block in the same picture as thecurrent block, assuming video encoder 200 codes CTUs and CUs in rasterscan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of thecoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagram illustrating an example QTBTstructure 130, and a corresponding CTU 132. The solid lines representquadtree splitting, and dotted lines indicate binary tree splitting. Ineach split (i.e., non-leaf) node of the binary tree, one flag issignaled to indicate which splitting type (i.e., horizontal or vertical)is used, where 0 indicates horizontal splitting and 1 indicates verticalsplitting in this example. For the quadtree splitting, there is no needto indicate the splitting type, since quadtree nodes split a blockhorizontally and vertically into 4 sub-blocks with equal size.Accordingly, video encoder 200 may encode, and video decoder 300 maydecode, syntax elements (such as splitting information) for a regiontree level of QTBT structure 130 (i.e., the solid lines) and syntaxelements (such as splitting information) for a prediction tree level ofQTBT structure 130 (i.e., the dashed lines). Video encoder 200 mayencode, and video decoder 300 may decode, video data, such as predictionand transform data, for CUs represented by terminal leaf nodes of QTBTstructure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplitting reach the minimum allowed binary tree leaf node size(MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). Theexample of QTBT structure 130 represents such nodes as having dashedlines for branches. The binary tree leaf node is referred to as a codingunit (CU), which is used for prediction (e.g., intra-picture orinter-picture prediction) and transform, without any furtherpartitioning. As discussed above, CUs may also be referred to as “videoblocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, then the node is not further split by thebinary tree, because the size exceeds the MaxBTSize (i.e., 64×64, inthis example). Otherwise, the leaf quadtree node will be furtherpartitioned by the binary tree. Therefore, the quadtree leaf node isalso the root node for the binary tree and has the binary tree depth as0. When the binary tree depth reaches MaxBTDepth (4, in this example),no further splitting is permitted. A binary tree node having width equalto MinBTSize (4, in this example) implies no further horizontalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize implies no further vertical splitting is permittedfor that binary tree node. As noted above, leaf nodes of the binary treeare referred to as CUs and are further processed according to predictionand transform without further partitioning.

In the current VVC specification and VTM (VVC test model) software, whenquantization is performed on certain rectangular blocks that satisfy thecondition of (log₂ (width)+log₂ (height)) not being divisible by 2, thedefault scaling and bitwise shift operations results in coefficientlevels that are 1/√{square root over (2)} times the required value (i.e.smaller). Thus, using the same default scaling and bitwise shiftoperation for blocks where (log₂ (width)+log₂ (height)) is divisible by2 as for blocks were rectangular blocks that satisfy the condition of(log₂ (width)+log₂ (height)) is not divisible by 2 may have undesirableresults. This is the result of using a shift parameter that is dependenton a (log₂ (width)+log₂ (height))/2 computation which is floored (e.g.,rounded down to the nearest integer value). In order to address thispotential problem, one example solution is to introduce a scaling by 181factor and right shift by 7 (i.e., division by 256), effectivelyintroducing 181/128≈√{square root over (2)} scaling for compensating thelower by 1/√{square root over (2)} in resulting levels from defaultscaling operations. The scaling by 181 introduces an increase in bitdepth for intermediate values of coefficients during quantization, whichmay undesirably increase memory bandwidth and computational complexity.The techniques of this disclosure may address some of theseshortcomings.

The transform shift parameter is computed by the following function inthe VTM software:

static inline int getTransformShift(const int channelBitDepth, constSize size, const int maxLog2TrDynamicRange) { returnmaxLog2TrDynamicRange − channelBitDepth − ((g_aucLog2[size.width] +g_aucLog2[size.height]) >> 1); }

In HEVC and VVC, every increase of 6 in quantization parameter (QP)corresponds to an increase of step size by a factor of 2 (i.e.,doubling). An increase of 3 of the quantization parameter corresponds toincreasing the step size by √{square root over (2)}. Decreasing thequantization parameter by 3 corresponds to scaling the quantization stepsize, and hence scaling the computed level by 1/√{square root over (2)}.This feature can be utilized with existing default scaling and shiftingfunctions to compensate for the decrease in level values by a factor of1/√{square root over (2)}.

For rectangular transform blocks whose aspect ratio does not satisfy thedivisible by two (log₂ (width)+log₂ (height)) parameter, video encoder200 and video decoder 300 may determine the QP used in the currentquantization and dequantization functions by mapping QP to QP-3. Videoencoder 200 and video decoder 300 may derive scaling and shiftingparameters based on the remapped QP, with the resulting coefficientsresulting in the required level.

Similarly, for such aspect ratio blocks, video encoder 200 and videodecoder 300 may determine QP by mapping QP to QP+3. In this case, the(log₂ (width)+log₂ (height)+1)/2 value that is rounded up to an integervalue, using a ceiling function (Ceil( )) is used, thus decreasing theright shift value by 1, which effectively doubles the value that isbeing right shifted. As the original levels with default scaling factoris 1/√{square root over (2)}, and the effective QP step size is1/√{square root over (2)} the original step size, the combined factor is½ and is compensated by a factor of 2 coming from the doubling of thecomputed value from decreased right shift amount by 1. The transformshift parameter can be computed with the following function followingthe syntax in VTM software.

static inline int getTransformShift(const int channelBitDepth, constSize size, const int maxLog2TrDynamicRange) { returnmaxLog2TrDynamicRange − channelBitDepth − ((g_aucLog2[size.width] +g_aucLog2[size.height] + 1) >> 1); }

The value of iTransformShift is obtained from the above function, andused in quantization scaling shift as described below for forwardquantization.const int iQBits=QUANT SHIFT+QP_per+iTransformShift;

Although some of the techniques above were described with respect toquantization, the techniques may also be used for determining modifiedQP values for dequantization. If the aspect ratio of a transform blocksfalls into the category described above (e.g., (log₂ (width)+log₂(height)) not being divisible by 2), the QP is modified as describedabove, and the shift amount in the dequantization process can use theupdated iTransformShift variable from the process described for forwardquant above.const int rightShift=(IQUANT_SHIFT−(iTransformShift+QP_per));

In cases of finer QP parameter usage, e.g. doubling of quantizer stepsize for every 12 steps, then the square root of 2 factor would beincorporated using QP-6 or QP+6, basically half of QP step size doublingincrement for QP parameters.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards and are applicable generally to video encoding and decoding.

In the example of FIG. 3, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,uncoded version of the current block from video data memory 230 and theprediction block from mode selection unit 202. Residual generation unit204 calculates sample-by-sample differences between the current blockand the prediction block. The resulting sample-by-sample differencesdefine a residual block for the current block. In some examples,residual generation unit 204 may also determine differences betweensample values in the residual block to generate a residual block usingresidual differential pulse code modulation (RDPCM). In some examples,residual generation unit 204 may be formed using one or more subtractorcircuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder20 and video decoder 30 may also support asymmetric partitioning for PUsizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value, or modified QP value, associated withthe current block. Video encoder 200 (e.g., via mode selection unit 202)may adjust the degree of quantization applied to the transformcoefficient block associated with the current block by adjusting the QPvalue associated with the CU. Quantization may introduce loss ofinformation, and thus, quantized transform coefficients may have lowerprecision than the original transform coefficients produced by transformprocessing unit 206. Quantization unit 208 may, for example, determineQP for a non-square, rectangular block of transform coefficients,determine a value for (log₂ (width)+log₂ (height), and in response tothe value not being divisible by 2, determine a modified QP for theblock of transform coefficients based on the QP.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Inverse quantization unit,like quantization unit 208, may also determine QP for a non-square,rectangular block of transform coefficients, determine a value for (log₂(width)+log₂ (height), and in response to the value not being divisibleby 2, determine a modified QP for the block of transform coefficientsbased on the QP.

Reconstruction unit 214 may produce a reconstructed block correspondingto the current block (albeit potentially with some degree of distortion)based on the reconstructed residual block and a prediction blockgenerated by mode selection unit 202. For example, reconstruction unit214 may add samples of the reconstructed residual block to correspondingsamples from the prediction block generated by mode selection unit 202to produce the reconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding blocks andthe chroma coding blocks.

In this manner, video encoder 200 represents an example of a device witha memory configured to store video data and one or more processorsimplemented in circuitry and configured to determine a quantizationparameter (QP) for a block of transform coefficients, wherein the blockof transform coefficients is a non-square, rectangular block; determinea value for (log₂ (width)+log₂ (height), wherein width represents awidth of the block of transform coefficients and height represents aheight of the block of transform coefficients; in response to the valuenot being divisible by 2, determine a modified QP for the block oftransform coefficients based on the QP; inverse transform the transformcoefficients to determine a block of quantized residual samples; anddequantize the quantized residual samples based on the modified QP todetermine a block of residual samples. Video encoder 200 may, forexample, output the decoded picture to a decoded picture buffer andencode one or more additional pictures based on the decoded picture.Video encoder 200 may additionally or alternatively quantize transformcoefficients using the modified QP.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 is describedaccording to the techniques of JEM and HEVC. However, the techniques ofthis disclosure may be performed by video coding devices that areconfigured to other video coding standards.

In the example of FIG. 4, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Prediction processing unit 304includes motion compensation unit 316 and intra-prediction unit 318.Prediction processing unit 304 may include additional units to performprediction in accordance with other prediction modes. As examples,prediction processing unit 304 may include a palette unit, anintra-block copy unit (which may form part of motion compensation unit316), an affine unit, a linear model (LM) unit, or the like. In otherexamples, video decoder 300 may include more, fewer, or differentfunctional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. CPB memory 320and DPB 314 may be provided by the same memory device or separate memorydevices. In various examples, CPB memory 320 may be on-chip with othercomponents of video decoder 300, or off-chip relative to thosecomponents.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a QP and/or transformmode indication(s). Inverse quantization unit 306 may, for example,determine QP for a non-square, rectangular block of transformcoefficients, determine a value for (log₂ (width)+log₂ (height), and inresponse to the value not being divisible by 2, determine a modified QPfor the block of transform coefficients based on the QP. Inversequantization unit 306 may use the modified QP, or in some examples theQP, associated with the quantized transform coefficient block todetermine a degree of quantization and, likewise, a degree of inversequantization for inverse quantization unit 306 to apply. Inversequantization unit 306 may, for example, perform a bitwise left-shiftoperation to inverse quantize the quantized transform coefficients.Inverse quantization unit 306 may thereby form a transform coefficientblock including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notneeded, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are needed, filterunit 312 may store the filtered reconstructed blocks to DPB 314. Asdiscussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured todetermine a quantization parameter (QP) for a block of transformcoefficients, wherein the block of transform coefficients is anon-square, rectangular block; determine a value for (log₂ (width)+log₂(height), wherein width represents a width of the block of transformcoefficients and height represents a height of the block of transformcoefficients; in response to the value not being divisible by 2,determine a modified QP for the block of transform coefficients based onthe QP; inverse transform the transform coefficients to determine ablock of quantized residual samples; and dequantize the quantizedresidual samples based on the modified QP to determine a block ofresidual samples.

FIG. 5 is a flowchart illustrating an example process for encoding acurrent block. The current block may include a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 2), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 5.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, uncodedblock and the prediction block for the current block. Video encoder 200may then transform and quantize coefficients of the residual block(354). As part of quantizing coefficients for a non-square, rectangularblock of transform coefficients, video encoder 200 may, for example,determine a QP, determine a value for (log₂ (width)+log₂ (height), andin response to the value not being divisible by 2, determine a modifiedQP, in accordance with techniques described herein, for the block oftransform coefficients based on the QP.

Next, video encoder 200 may scan the quantized transform coefficients ofthe residual block (356). During the scan, or following the scan, videoencoder 200 may entropy encode the coefficients (358). For example,video encoder 200 may encode the coefficients using CAVLC or CABAC.Video encoder 200 may then output the entropy coded data of the block(360).

FIG. 6 is a flowchart illustrating an example process for decoding acurrent block of video data. The current block may include a current CU.Although described with respect to video decoder 300 (FIGS. 1 and 3), itshould be understood that other devices may be configured to perform amethod similar to that of FIG. 6.

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data forcoefficients of a residual block corresponding to the current block(370). Video decoder 300 may entropy decode the entropy coded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (372). Video decoder 300 may predictthe current block (374), e.g., using an intra- or inter-prediction modeas indicated by the prediction information for the current block, tocalculate a prediction block for the current block.

Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thecoefficients to produce a residual block (378). As part of inversequantizing coefficients for a non-square, rectangular block of transformcoefficients, video decoder 300 may, for example, determine a QP,determine a value for (log₂ (width)+log₂ (height), and in response tothe value not being divisible by 2, determine a modified QP, inaccordance with techniques described herein, for the block of transformcoefficients based on the QP. Video decoder 300 may ultimately decodethe current block by combining the prediction block and the residualblock (380).

FIG. 7 is a flowchart illustrating an example video decoding techniquedescribed in this disclosure. The techniques of FIG. 7 will be describedwith reference to a generic video decoder, such as but not limited tovideo decoder 300. In some instances, the techniques of FIG. 23 may beperformed by video encoder 200 (e.g., by the decoding loop of inversequantization unit 210 and inverse transform processing unit 212).

In the example of FIG. 7, the video decoder determines a quantizationparameter (QP) for a non-square, rectangular block of transformcoefficients (390).

The video decoder determines a value for (log₂ (width)+log₂ (height)(392). In this instance, width represents a width of the block oftransform coefficients, and height represents a height of the block oftransform coefficients;

In response to the value not being divisible by 2, the video decoderdetermines a modified QP for the block of transform coefficients basedon the QP (394). To determine the modified QP based on the QP, the videodecoder may, for example, map the QP to the modified QP. In otherexamples, to determine the modified QP based on the QP, the videodecoder may map the QP to QP-3.

The video decoder inverse transforms the transform coefficients todetermine a block of quantized residual samples (396). The video decoderdequantizes the quantized residual samples based on the modified QP todetermine a block of residual samples (398). The video decoder maydetermine a scaling parameter based on the modified QP and dequantizethe quantized residual samples based on the scaling factor to determinethe block of residual samples. The video decoder may determine ashifting parameter based on the modified QP and dequantize the quantizedresidual samples based on the shifting parameter to determine the blockof residual samples.

The video decoder adds the block of residual samples to a predictionblock to determine a reconstructed block. The video decoder may performone or more filtering operations on the reconstructed block to determinea decoded block of video data and output a decoded picture that includesthe decoded block of the video data.

The video decoder may, for example, output the decoded picture bydisplaying the decoded picture or by storing the decoded picture forlater display. The video decoder may also output the decoded picture bystoring the decoded picture in a decoded picture buffer and decoding oneor more additional pictures based on the stored decoded picture. Ininstances where the video decoder is part of a video encoder, the videodecoder may output the decoded picture by storing the decoded picture ina decoded picture buffer and encoding one or more additional picturesbased on the stored decoded picture.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can include one or more of RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage, or other magnetic storagedevices, flash memory, or any other medium that can be used to storedesired program code in the form of instructions or data structures andthat can be accessed by a computer. Also, any connection is properlytermed a computer-readable medium. For example, if instructions aretransmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave, then the coaxialcable, fiber optic cable, twisted pair, DSL, or wireless technologiessuch as infrared, radio, and microwave are included in the definition ofmedium. It should be understood, however, that computer-readable storagemedia and data storage media do not include connections, carrier waves,signals, or other transitory media, but are instead directed tonon-transitory, tangible storage media. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc, where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

Instructions may be executed by one or more processors, such as one ormore DSPs, general purpose microprocessors, ASICs, FPGAs, or otherequivalent integrated or discrete logic circuitry. Accordingly, the term“processor,” as used herein may refer to any of the foregoing structureor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: determining a first quantization parameter (QP) for a blockof first transform coefficients, wherein the block of the firsttransform coefficients is a non-square, rectangular block; determiningthat a value for (log₂ (width)+log₂ (height)) is not divisible by 2,wherein width represents a width of the block of the first transformcoefficients and height represents a height of the block of the firsttransform coefficients; in response to the value not being divisible by2, mapping the first QP to QP-3 to determine a modified QP; inversetransforming the first transform coefficients to determine a block offirst quantized residual samples; dequantizing the first quantizedresidual samples based on the modified QP to determine a block of firstresidual samples; determining a second QP for a block of secondtransform coefficients, wherein the block of the second transformcoefficients is a second non-square block; inverse transforming thesecond transform coefficients to determine a block of second quantizedresidual samples; determining that a second value for (log₂ (width2)+log₂ (height2)) is divisible by 2, wherein width2 represents a widthof the block of the second transform coefficients and height2 representsa height of the block of the second transform coefficients; and inresponse to the second value being divisible by 2, dequantizing thesecond quantized residual samples based on the second QP to determine ablock of second residual samples.
 2. The method of claim 1, furthercomprising: determining a scaling parameter based on the modified QP;and dequantizing the first quantized residual samples based on thescaling factor to determine the block of the first residual samples. 3.The method of claim 1, further comprising: determining a shiftingparameter based on the modified QP; and dequantizing the first quantizedresidual samples based on the shifting parameter to determine the blockof the first residual samples.
 4. The method of claim 1, furthercomprising: adding the block of the first residual samples to aprediction block to determine a reconstructed block.
 5. The method ofclaim 4, further comprising: performing one or more filtering operationson the reconstructed block to determine a decoded block of video data;and outputting a decoded picture comprising the decoded block of thevideo data.
 6. The method of claim 5, wherein outputting the decodedpicture comprises storing decoded picture in a decoded picture buffer,the method further comprising: encoding one or more additional picturesbased on the decoded picture.
 7. The method of claim 5, whereinoutputting the decoded picture comprises displaying the decoded picture.8. A device for decoding video data, the device comprising: a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: determine a first quantization parameter(QP) for a block of first transform coefficients, wherein the block ofthe first transform coefficients is a non-square, rectangular block;determine that a value for (log₂ (width)+log₂ (height)) is not divisibleby 2, wherein width represents a width of the block of the firsttransform coefficients and height represents a height of the block ofthe first transform coefficients; in response to the value not beingdivisible by 2, map the first QP to QP-3 to determine a modified QP;inverse transform the first transform coefficients to determine a blockof first quantized residual samples; dequantize the first quantizedresidual samples based on the modified QP to determine a block of firstresidual samples; determine a second QP for a block of second transformcoefficients, wherein the block of the second transform coefficients isa second non-square block; inverse transform the second transformcoefficients to determine a block of second quantized residual samples;determine that a second value for (log₂ (width 2)+log₂ (height2)) isdivisible by 2, wherein width2 represents a width of the block of thesecond transform coefficients and height2 represents a height of theblock of the second transform coefficients; and in response to thesecond value being divisible by 2, dequantize the second quantizedresidual samples based on the second QP to determine a block of secondresidual samples.
 9. The device of claim 8, wherein the one or moreprocessors are further configured to: determine a scaling parameterbased on the modified QP; and dequantize the first quantized residualsamples based on the scaling factor to determine the block of the firstresidual samples.
 10. The device of claim 8, wherein the one or moreprocessors are further configured to: determine a shifting parameterbased on the modified QP; and dequantize the first quantized residualsamples based on the shifting parameter to determine the block of thefirst residual samples.
 11. The device of claim 8, wherein the one ormore processors are further configured to: add the block of the firstresidual samples to a prediction block to determine a reconstructedblock.
 12. The device of claim 11, wherein the one or more processorsare further configured to: perform one or more filtering operations onthe reconstructed block to determine a decoded block of video data; andoutput a decoded picture comprising the decoded block of the video data.13. The device of claim 12, wherein to output the decoded picture, theone or more processors are further configured to store the decodedpicture in a decoded picture buffer, wherein the one or more processorsare further configured to: encode one or more additional pictures basedon the decoded picture.
 14. The device of claim 12, further comprising:a display configured to display decoded video data; wherein to outputthe decoded picture, the one or more processors are further configuredto display the decoded picture on the display.
 15. The device of claim8, wherein the device comprises one or more of a camera, a computer, amobile device, a broadcast receiver device, or a set-top box.
 16. Acomputer-readable storage medium storing instructions that when executedby one or more processors cause the one or more processors to: determinea first quantization parameter (QP) for a block of first transformcoefficients, wherein the block of the first transform coefficients is anon-square, rectangular block; determine that a value for (log₂(width)+log₂ (height)) is not divisible by 2, wherein width represents awidth of the block of the first transform coefficients and heightrepresents a height of the block of the first transform coefficients; inresponse to the value not being divisible by 2, map the first QP to QP-3to determine a modified QP; inverse transform the first transformcoefficients to determine a block of first quantized residual samples;dequantize the first quantized residual samples based on the modified QPto determine a block of first residual samples; determine a second QPfor a block of second transform coefficients, wherein the block of thesecond transform coefficients is a second non-square block; inversetransform the second transform coefficients to determine a block ofsecond quantized residual samples; determine that a second value for(log₂ (width 2)+log₂ (height2)) is divisible by 2, wherein width2represents a width of the block of the second transform coefficients andheight2 represents a height of the block of the second transformcoefficients; and in response to the second value being divisible by 2,dequantize the second quantized residual samples based on the second QPto determine a block of second residual samples.
 17. Thecomputer-readable storage medium of claim 16, storing furtherinstructions that when executed by the one or more processors cause theone or more processors to: determine a scaling parameter based on themodified QP; and dequantize the first quantized residual samples basedon the scaling factor to determine the block of the first residualsamples.
 18. The computer-readable storage medium of claim 16, storingfurther instructions that when executed by the one or more processorscause the one or more processors to: determine a shifting parameterbased on the modified QP; and dequantize the first quantized residualsamples based on the shifting parameter to determine the block of thefirst residual samples.
 19. The computer-readable storage medium ofclaim 16, storing further instructions that when executed by the one ormore processors cause the one or more processors to: add the block ofthe first residual samples to a prediction block to determine areconstructed block; perform one or more filtering operations on thereconstructed block to determine a decoded block of video data; andoutput a decoded picture comprising the decoded block of the video data,wherein outputting the decoded picture comprises displaying the decodedpicture.
 20. An apparatus for decoding video data, the apparatuscomprising: means for determining a first quantization parameter (QP)for a block of first transform coefficients, wherein the block of thefirst transform coefficients is a non-square, rectangular block; meansfor determining that a value for (log₂ (width)+log₂ (height)) is notdivisible by 2, wherein width represents a width of the block of thefirst transform coefficients and height represents a height of the blockof the first transform coefficients; means for mapping the first QP toQP-3 to determine a modified QP in response to the value not beingdivisible by 2; means for inverse transforming the first transformcoefficients to determine a block of first quantized residual samples;means for dequantizing the first quantized residual samples based on themodified QP to determine a block of first residual samples; means fordetermining a second QP for a block of second transform coefficients,wherein the block of the second transform coefficients is a secondnon-square block; means for inverse transforming the second transformcoefficients to determine a block of second quantized residual samples;means for determining that a second value for (log₂ (width 2)+log₂(height2)) is divisible by 2, wherein width2 represents a width of theblock of the second transform coefficients and height2 represents aheight of the block of the second transform coefficients; and means fordequantizing the second quantized residual samples based on the secondQP to determine a block of second residual samples in response to thesecond value being divisible by
 2. 21. The apparatus of claim 20,further comprising: means for determining a scaling parameter based onthe modified QP; and means for dequantizing the first quantized residualsamples based on the scaling factor to determine the block of the firstresidual samples.
 22. The apparatus of claim 20, further comprising:means for determining a shifting parameter based on the modified QP; andmeans for dequantizing the first quantized residual samples based on theshifting parameter to determine the block of the first residual samples.